Electromagnetic induction apparatus



Sept. 19, 1950 G. G. SOMERVILLE ELECTROMAGNETIC INDUCTION APPARATUS 4Sheets-Sheet 1 Filed June 1, 1944 Inventor Gareth G. SomerviHe s ,Hthew-neg p 19, 1950 s. G. SOMERVILLE 2,523,071

ELECTROMAGNETIC INDUCTION APPARATUS Filed June 1, 1944 4 Sheets-Sheet 2InQen'bor: v Gareth G. SomeT-ville,

H is Attorney.

Sept. 19, 1950 G. G. SOMERVILLE ELECTROMAGNETIC INDUCTION APPARATUS*ilad June 1, 1944 4 Sheets-Sheet I5 Gareth G. Somervi I le,

His Attorneg.

p 1950 G. G. SOMERVILLE 2,523,071

ELECTROMAGNETIC INDUCTION APPARATUS Filed June 1, 1944 4 Sheets-Sheet 4Inventor: Gareth G. Somerville,

11ft! 1 n t]; H a. b W UMAM H/ His Attorne g.

Patented Sept. 19, 1950 ELECTROMAGNETIC INDUCTION APPARATUS Gareth G.Somerville, Pittsfleld, Mass., assignor to General Electric Company, acorporation of New York Application June 1, 1944, Serial No. 538,303

2 Claims. (Cl. 175-356) My invention relates to electromagneticinduction apparatus, to magnetic cores of the curved iron type, and to amethod of forming the curved iron type core.

Heretofore it has been customary to form electromagnetic inductionapparatus, particularly for application in the low frequency or powerfrequency field, with magnetic cores formed of a plurality of assembledflat punchings, or by flatwise bending or winding a strip of magneticmaterial to produce a bent or wound type core. In the high frequencyfield the cores have been produced of powdered iron bonded together witha suitable binder.

A core formed of highly directional steel which is wound in the form ofa spiral so that the flux will pass along the most favorable magneticdirection throughout the entire periphery of the core will have arelatively low core loss, and such a core has been used for sometime ininstrument type bushing current transformers since with this type oftransformer it is not necessary to disturb the core to assemble it withthe primary winding, as the primary winding usually includes a singleconductor which passes through the ring shaped core, with a few turns ofsecondary distributed through and around the ring shaped core. Also,although it has been known since the latter part of the last centurythat cores may be made of the flatwise bent type, for instance as shownin British Patent 7,856 of 1889, it has been to suitably align theadjacent ends of the corresponding sheets from each of the groups. Thecore may then be expanded to the desired shape, annealed, and afterannealing, one group is disassembled from the second to form two coreportions which portions may then be reassembled around the preformedconductive winding structure.

It is an object of the present invention to provide an improved methodof forming a core of the above-mentioned type.

It is another object of my invention to provid an efiicient method offorming a curved iron type magnetic core which may be assembled with apreformed conductive winding structure to produce an efiicientelectromagnetic induction apparatus.

It is a further object of my invention to provide an electromagneticinduction apparatus with an improved core of the curved iron type.

Further objects and advantages of my invention will become apparent fromthe following description referring to the accompanying drawing, and thefeatures of novelty which characterize my invention will be pointed 'outwith particularity in the claims annexed to and forming a part of thisspecification.

customary to form cores for electromagnetic incore for electromagneticinduction apparatus which may be eiiiciently applied to a relativelywide range of transformer sizes and which includes at least two groupsof magnetic sheets which have been precut to the desired size. Thesheets are then assembled by inserting first sheets of one group andthen sheets from the other group within a ring shaped member so as toproduce a generally circular shaped closed core construction. Pressuremay then be applied to the inside and outside surfaces of the ring so asing oven; Fig. 6 is a sectional side elevation of one of the coresassembled around one leg of the conductive winding and another core inthe process of assembly; Fig. 6a is an enlarged view of a portion of thejoint of Fig. 6; Fig. 7 illustrates a machine which may be used to bendthe groups of sheets; Fig. 8 illustrates a modified type of coreconstruction which may be formed according to my improved method; Fig. 9illustrates two groups of magnetic sheets which form the core of Fig. 8;Fig. 10 illustrates another core construction which is formed accordingto my invention; Fig. ll illustrates two groups of magnetic sheets usedto form the core of Fig. 10; Fig. 12 illustrates the two groups ofmagnetic sheets of Fig. 11 as they are assembled before being flatwisebent; Figs. 13 to 16 illustrate groups of magnetic sheets being bent andformed according to a modification of my improved method; Fig. 1'1illustrates the two U-shaped core portions formed according to themethod of Figs. 13 to 16, the core being ready for its strain-reliefanneal; Fig. 18 is a sectional side elevation of a magnetic core formedaccording to a modification of my improved method; Fig. 19 illustrates agroup of magnetic sheets used to form one of the core portions of Fig.18; Fig. 20 illustrates the group of sheets of Fig. 19 during theprocess of being tlatwise bent; Figs. 21 to 23 illustrate further stepsin bending and forming the group of magnetic sheets of Fig. 20; andFigs. 24 to 2'1 illustrate further modifications of the method offorming the core.

Referring to Fig. 1 of the drawing, I have illustrated anelectromagnetic induction apparatus having a preformed coil winding 80with two similar cores Ii and I! surrounding leg! II and M,respectively, of the preformed conductive winding structure ll. Each ofthe core portions Ii and 32 includes generally U-shaped core portions 85and 30 with a suitable butt joint 31 between corresponding ends of thelegs of the generally U-shaped core portions. In Fig. l, I haveillustrated the joint 31 as being what I term a searfed butt joint, butit will be seen that, as the description proceeds, any suitable type ofjoint construction may be produced according to my improved method.Although two cores are shown as linking a single conductive windingstructure, it will be understood that my improved method may be used toform any suitable number of conductive winding structures and to produceany suitable type of electromagnetic induction apparatus, such as atransformer or reactor. Furthermore, my invention may be used to producean electromagnetic induction apparatus for a wide range of sizes andapplications, such as cores employing relatively thin magnetic stripssuch as 2 mil to produce relatively small transformers for highfrequency applications, to cores using relatively thick strip such as 14mil for the larger type transformers.

In order to produce the core illustrated in Fig. l, I provide two groupsof magnetic sheets II and 39, as is shown in Fig. 2. These sheets ofmagnetic material may be formed of any suitable strip such as highlydirectional strip steel having the most favorable magnetic directionrunning longitudinally of the sheets. The two groups It and I! ofmagnetic sheets have approximately the same number and the sheets havesuch length so that corresponding sheets from each group when assembledwill have a total length equal to the peripheral distance around thecore at that particular layer in the finished core. Thus given the sizeof the finished core the designer can calculate the length of each ofthe sheets in the two groups which will be used to form the finishedcore. It will also be seen that by the use of various combinations oflengths of sheets in the two groups, any suitable type of scarfed orbutt or overlap Joint may be provided as will be brought out moreclearly below.

In the production of a scarfed butt joint as shown in Fig. 1 andindicated by the numeral I1, I provide the one group It with each sheethaving the same length. The sheets forming the group It, however, haveprogressively different lengths, the shortest length being used at theinner perimeter of the finished core and the corrsponding longer lengthsbeing used toward the outer periphery. The magnetic sheets may be cut tosize in any suitable manner such as measuring by hand and cutting to theproper size or they may be cut on my improved index shearing machine,described and claimed in my application Serial No. 539,255, filed June8, 1944, now Patent No. 2,389,617, and assigned to the same assignee asthis present invention. Such an index shearing machine will producesheets ofprogressivelydiflerentlengthssoastoproduce the group 35.Furthermore, openings or holesuandll maybepimchedineachoithesheetsastheyarecut. Theseholesmaybe punched in any suitable place on thesheet and inthetwogroumofsheetsllandlltheboluarepunchedinthelongitudinalcenterofeach of the sheets.

In order to assemble the two groups of sheets 88 and II to produce thecore as illustrated in Flg.l,thesheetsafterbeingassembledinthemannerillustratedinl'igJareflatwisebentto produce two generally U-shapedcore portions.

This bending may be accomplished in any suit able manner and when thesheets are relatively thinandflexibletheymaybebentbyhand. Thesheetsmayofcoursealsobebentinasuitable machine. as will be describedbelow in connection with Fig. 7. However, even though the sheets are cutas accurately as possible and theholesareplacedasnearaspossibleinthelongitudinal center of the sheets,when they are bent to form two generally U-shaped members, theendsofthesheetsmaynotbeplacedintheexact desired position in relation tothe corresponding sheet of the adjacent leg of the other core portion sothat the corresponding sheets may abut relatively tightly together toproduce a low loss joint In order therefore to insure a relatively lowloss joint by providing a relatively tight butt joint between the endsof corresponding sheets in the adjacent legs of each of the generallyU-shaped core portions, 1 suitably appl pressure at least in a directiongenerally parallel with the magnetic sheets in the legs of the U-shapedmembers so that the adjacent ends of corresponding sheets which are tofit relatively tightly together will be put in equivalent planes. Theapplication of this pressure may be accomplished in any suitable mannerand in Figs. 3 and 4, I have illustrated structure for accomplishingthis step in my improved method.

As will be seen with reference to Fig. 2 the group I. is assembled withthe openings II in alignment with the pin 42 passing through the opening4.. Similarly a pin 0 passes through the openings ll of the sheets ofthe group It. The pins extend outwardly from opposite surfaces of amandrel 64 so that upon application of the pressure to each of thegroups in a direction toward the mandrel 44 the sheets will each be bentas a group to form two generally U-shaped portions. While the sheets arein this position they may be introduced into the machine, as isillustrated in Fig. 3, which includes two diametricaliy opposed blocks 5and It. the blocks having suitable openings to receive the ends of thepins 41 and I. In order that pressure may be applied to the coreportions in a general direction parallel with the plane of the sheets inthe legs of the core portions, blocks 45 and 46 are relatively movable.Thus the block 45 may be relatively stationary and the block 45cooperates with an end of a screw 41. The upper end of the screwincludes a nut 0 which is internally threaded with the screw 41. Theouter end of theeerewtlhaeahandiellwhichmaybe-diametricallyopposedandpositionedsothat force may be applied to thecore portions in a general direction perpendicular to the 1m of thegenerally U-shaped core portions. The blocks II and II cooperate withscrews I and II, the screws passing through threaded openings in thestationary supports I2 and II. It will beseenthatbyturningthescrewsilandtLthelegsol.thecoreportlonsmaybeforcedtowardthe mandrel.Itwillbeunderstoodthatthecore may be suitably formed by rotating each ofthe screws 41, GI, and I progressively or together in suitable amountsuntil the core attains the positionasisillustratedinfi8.4. ItwillbeseeninFlgs.3and4thatastrap62 ofsuitahlematerial such as metal alreadysurrounds the core portions, the ends of the strap having openingsthrough which the screw 41 extends. Thus oneendofthestrapispassedovertheendofthe' screw l1 and the strap is thenwrapped completelyaroundtheclosedcore. Anotherendllofthe strap then hasan opening through which the screw 41 extends. A nut 64 is placedunderneath theendsoithestrapanditwillbeseenupon turning,thenutsoastoforcetheends62and 88 away from the core, that the strap maybe placed relatively tightly around the core portions. The strap maythen be spot welded at the points it and the strap then cut as indicatedby the numeral It. 4.

The core portions with their ends suitably positioned in abuttingrelation are now in condition for obtaining the strain-relief anneal,and Pig. illustrates the core stacked in a furnace to obtain thestrain-relief anneal. A weight 61 may be placed on the core so astoholdthe sheets in place until the anneal is completed. After the core hasbeen removed from the strain-reliefannealfurnaceitisreadytobeassembledwith a performed coil winding. Itwill be understood that the strain-relief anneal gives each of thesheets a permanent set in the relative positionstheyhaveinthefurnacesothatthe sheets will naturally tend to maintainthemselves in same relative position they had in the furnace.

sheets will not be disturbed upon removal of the supporting band 62. thepins .2 and 43 upon re moval may be replaced with rivets I. and H,respectively. Any other suitable means may be provided to hold thesheets in their proper position. The band '2 may then be removed and thegenerally U-shaped core portions bled as is illustrated in Fig. 6. Thecore portions may then be introduced with the corresponding legs of eachof the generally U-shaped core portions in abutting relation and withone of the l ss prolecting into the window of the preformed coil.Abandnmaythenbeplacedaroundthe U-shaped core portion and pulledrelatively tightly together and then attached in anysuitablemannersuchasbyspotweldingtheband portiom as is illustrated bythe numeral II.

7 "However. in order to further insure that the v I theadiaeent ends.ltand .ll'were toiltrelativelyflsh lytogethertoformalowlo-buttiointacccrdingtothemethod de-.

above.solongasthesheetsarenotdis- I thecore portions may be disassembledand tea-ambled around the preformedcoil as ilin-Pig. 6, and thecorresponding sheets of the generally U-shaped core portions arelatively tight butt joint in the positionthey had when the core wasrethe strain-relief anneal furnace. understood that with a scarfed buttas shown in Fig. 6. since the sheets have the the entire end edge ofeach sheet not be in one plane as is indicated for conof tion in Fig. 6,but the Joint iliustra The ends could. however. if in one substantialplane by tio As ned Pig. thegroups of sheets are assembled they may bein any suitable manner, and in- Fig. 7,1 have-illustrated a machine forout this bending operation. The machine includes two relatively movableU-shaped form members ll and II. It will be understood that the internalsurface of the U-shaped memll 81 has a suitable size for producing theparticular core construction desired. Operatagg sgs above in connectionwith sired position until they are annealed.

As has been mentioned, any suitable type of Joint construction may beformed in the core according to my'invention, and in Fig. 8, I haveillustrated a construction having a butt joint which instead of beingscarfed is perpendicular to the plane of the sheets in the leg portions.Thin in Fig. 8. I have illustrated two core portions I! and I with buttjoints l1 and Cl between the adjacent ends of correspondinglegs of thetwo generally U-shaped core portions. The core portions II and II areformed by bending flatwise two groups of magnetic sheets as describedabove in connection with Figs. 1 through '1. The two groups that formthe core portions of Fig. 8 are illustrated in Fig. 9 and are identifiedby the numerals II and II.

' In order to produce the particular joint configuration it will be seenthat both oi the groups 8! and I are formed of sheets havingprogressively different lengths. the smaller sheets of each groupforming the inner layer of the finished core and the longer sheetsforming the outer layer. The sheets are also formed with openings II andI! in the longitudinal center line of the sheets to facilitate stackingand for accommodating rivets II. The sheets may also be formed ifdesired with openings or holes 84 and II near the ends of the sheet. Theholes in each of the sheets are placed the same distance from the endsof the sheets so that when the groups arebentintheformofthe U's theholes will be ingeneralalignmentsothatrivets maybe passed through theholes. It will be understood thattheserivetsmay be introducedatanysuitable time during the production of the cores such as after they areremoved from the strain-relief anneal. Instead of rivets any other meansmay be used for binding the sheets together, such as by applying a headof weld metal as is shown at Ill in Fig. 24.

I Fig. 10, I have illustrated a core construc tion formed according tomy improved method which core has an overlap butt joint. The coreincludes two generally U-shaped core portions 01 and 98 with the endsof'a suitable number of layers in each of the portions being staggered.Thus one layer 99 of the core portion ll extends beyond the ends of theadjacent layers Ill. Similarly a layer IOI of the adjacent leg of thecore portion 90 extends beyond a layer I02 of the core portion 98. Inorder that the projecting layers will be relatively stiff and will findtheir suitable position in relation to adjacent layers when the core isassembled around the preformed coils, any suitable number of magneticsheets may be employed to produce each of these layers, and when using14 mil strip two to six magnetic sheets for each of the layers is asuitable number.

In order to produce the core portions 91 and 98, two groups of magneticsheets III and I are cut as is illustrated in Fig. 11. These sheets maybe cut in any suitable relative lengths in order to produce the desiredoverlapping construction, and since the overlap joint is of the generalscarfed type in Fig. both of the groups I02 and I04 are formed of sheetshaving progressively different lengths. In order to produce the overlapjoint the sheets of the groups III! and I when they are out are providedwith holes I and I06, respectively, which holes are offset the sameamount from the longitudinal center of the sheets. The sheets may be cutwith the offset holes in any suitable manner such as by the machinedescribed and claimed in my patent application Serial No. 539,255,referred to above.

' 8 downwardly as shown by the arrow, the group of sheets I will beflatwise bent into a generally U-shaped configuration, as is illustratedin Fig. 14. It will also be seen that the forming piston or body III hassurfaces III in a plane of the finished scarfed butt joint 21 of theconstruction illustrated in Fig. 1. Thus by pressing on the ends of thesheets by the surfaces Ill the ends, or corresponding edges, will bemade to lie in a single plane. In order to suitably support the sheets,the members H2 and III are movable in a direction at right angles to themovement of the piston III. The walls H2 and III may be moved in anysuitable manner such as by connection to screws Iii and Ill,respectively. It will be understood that pressure may The sheets arethen assembled by longitudinally reversing the sheets of the variouslayers and the general idea of so assembling magnetic sheets to producean overlap butt joint is described and claimed in my application SerialNo. 536,748, referi ed to above. The sheets of groups I03 and I areassembled on pins 42 and 43 of the mandrel 44. It will be seen that thelayers are assembled with adjacent layers having ends projecting inopposite directions. Thus the first layer 99 has the longer side thereofin relation to the opening I" projecting' to the left of the pin 42,while the adjacent layer IOII has its longer side projecting to theright of the pin. The sheets such as four to six at a time may beassembled in this manner to provide a plurality of layers withoverlapping ends. The sheets may then be fiatwise curved and thenassembled together in the machines as illustrated in Figs. 3 and 4 so asto relatively tightly butt the corresponding layers of each of theadjacent legs of the U-shaped portions.

As has been mentioned above the cores may be assembled flatwise bent andthen pressure applied to the ends of the sheets forming the two legs ofthe generally U-shaped portions in any suitable manner and in Figs. 13to 16, I have illustrated another method of bending and applying thepressure to a group of sheets. Thus referring to Fig. 13 the group ofsheets 29 is assembled with a pin IIII passing through the openings H.The pin IIII extends from a forming piston III, and the stack 38 issupported on the edges of vertical side members H2 and III of a formingjig. Upon pushing the piston III be applied by the piston ill and theblocks H2 and III moved toward the core simultaneously or progressivelyso as to produce the desired butt joint. In order to hold the varioussheets in the desired position after this position has been produced dueto the pressure of the piston III and the blocks H2 and III, bracketmembers Ill and III ar provided between the adjacent surfaces of thecore portion and the blocks H2 and III. It will be seen that the bracketportions Ill and Ill are within the jig before the group of sheets 3! isforced into the jig. Connecting bars II! may be placed between thebrackets Ill and III and welded thereto so as to tightly hold the sheetsin the position as is illustrated in Fig. 14. It will be understood thatsimilar bars II! may be placedon the opposite side.

In order to produce the U-shaped core portion which cooperates with theone shown in Fig. 14 to produce a completed magnetic core, a group ofsheets 28 is similarly formed as is illustrated in Figs. 15 and 16.Since a scarfed butt joint is being produced when the group oflaminations II is formed in a general u-shape with the legs extendingupwardly, a piston I2. is provided with surfaces I2I which surfaces arein a different plane from the surfaces Ill. The surfaces I2I, however,are suitably formed relative to the surfaces II that upon the U-shapedcore portion as shown in Fig. 16 being inverted, the edges of the sheetsproduced by the surfaces I2I will abut relatively tightly with the edgesof the sheets produced by the surfaces I it. After the core portion hasbeen formed as is illustrated in Figs. 15 and 16 the core portions I22and I2! may be assembled as is illustrated in Fig. 17 and placed in anannealing furnace to be given a strain-relief anneal. When the coreportions I22 and I2! are assembled in the manner illustrated in Fig. l!with the edges I24 and I2! in abutting relation the corresponding sheetsof the two legs of each of the core portions will be caused to butt eventighter together during the strain-relief anneal. After annealing, thecore portions I22 and I2! may be removed and assembled around thepreformed coil as is described above in connection with Fig. 6.

It is to be understood, however, that instead of assembling the coreportions I22 and I22 to-- gether before placing in the strain-reliefanneal furnace, the core portions I22 and I23 may be separately stackedand placed in the annealing furnace and then removed and assembledtogether with a coil winding.

It will be understood that any other suitable type of joint may beformed according to the method described above in connection with Figs.13 through 16, and in Fig. 25, I have illustrated 9 a pistonconstruction I26 for forming a butt joint on a core portion I21 whichjoint is in a plane substantially perpendicular to the plane of thesheets in the legs of the core portion.

In Figs. 26 and 27. I have illustrated a modifled method of alignin theends of a core portion which includes providing openings I28 in a groupof laminations I29 suitably positioned so that after the group of sheetsis bent to form a U-shaped core the openings I28 will be placed ingeneral alignment. The sheets may then be suitably manipulated in casethe holes of each of the sheets do not line up properly so that a rivetI23 may be introduced through the holes when they are placed inregistry. This will produce a joint construction in which the edges areplaced in substantially a single plane, although the edges may not bequite as accurately positioned as they may be by the method whichincludes applying a force to the sheets in the manner described above inconnection with Figs. 1 through '7, or Figs. 13 through 16.

In Figs. 18 to 23, I have illustrated a core construction and a methodof producing the core when the groups of laminations are relatively longand flexible. Thus Fig. 18 illustrates a core including core portionsI30 and I3I each of which has a generally U-shaped construction. Each ofthe core portions I30 and I3I is formed by bending a group oflaminations of progressively different lengths, asis illustrated in Fig.19. The group of sheets I32 is assembled by placing the adjacent ends atone end I33 in alignment. This may be accomplished by having openingsI34 placed close to the ends of the sheets, each of the openings I34 ofeach sheet being the same distance from the end of the sheet. A pin I35may then be passed through the openings and a clamp I36 attached toopposite sides of the group. The sheets may then be bent with a secondclamp I31 placed on the opposite sides of the other end I38 as isillustrated by the dotted lines in Fig. 20. The group of sheets I32 maythen be given any suitable shape as is illustrated in Figs. 19 to 23.Thus the central portions of the sheet are held relatively straightthrough movable blocks I39 and the ends are formed into right angularlyextending legs by means of movable pistons I40. The core may then besupported in that position through the plates I39 and a bracketincluding plates HI and interconnecting rods I42. The core may then beannealed in this position, and after-annealing it can be assembled witha preformed coil. Two core portions as shown in Fig. 23 may be stackedtogether and then annealed, if desired. It will be understood that thecore construction described in Figs. 18 to 23 may be employed where thesheets are relatively long and relatively flexible.

Although I have shown and described particular embodiments of myinvention, I do not desire to be limited to the particular embodimentsdescribed, and I intend in the appended claims to 10 cover allmodifications which do not depart from the spirit and scope of myinvention.

What I claim as new and desire to secure by Letters Patent 01' theUnited States, is:

1. A curved iron type core including two generally U-shaped coreportions assembled to provide a closed magnetic core, each of said coreportions comprising a plurality of .nested flatwise curved strain-freestrips of magnetic material providing continuous magnetic paths atcorners, the-strips of one of said portions all being the same lengthwith their centers in radial alignment whereby their ends are stepped,the strips of the other of said portions having their centers in radialalignment and being of such diii'erent lengths that their ends arestepped in complementary iashion to the ends of the equal length strips,said portions being forced together whereby said stepped ends formprogressively staggered closely fitting overlapping scarfed butt joints.

GARETH G. SOMERVILLE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 523,572 Hassler July 24, 18941,102,513 Johannesen July '7, 1914 1,285,996 Hensley Nov. 26, 19181,858,225 Frederick May 10, 1932 1,935,426 Acly Nov. 14, 1933 2,058,362Smalley Oct. 20, 1936 2,066,186 Mitchell Dec. 29, 1936 2,288,855Steinmayer July I, 1942 2,290,680 Franz July 21, 1942 2,293,951 SeastoneAug. 25,1942 2,318,095 Putnam May 4, 1943 2,333,995 Gaynor' Nov. 9, 19432,380,300 Gaston "July 10, 1945 2,456,457 Somerville Dec. 14, 19482,456,458 Somerville Dec. '14, 1948 FOREIGN PATENTS Number Country Date7,856 Great Britain May 10, 1889 106,986 Great Britain June 14, 191'!364,346

Germany Nov. 23, 1922

